Nikkei slip as investors pocket quick gains on Softbank, Topix firmer

TOKYO, Sept 22 (Reuters) - Japan's Nikkei share average dropped on Monday as investors booked gains in heavyweight Softbank after the listing of Alibaba Group Holding Ltd , but the broader market held firmer near six-year high. The Nikkei declined 0.7 percent to 16,205.90, with a 6.1 percent slide in Softbank shares accounting for more than a half of the benchmark's fall. Softbank, which holds a 32 percent stake in Alibaba, had surged 30 percent over the past six weeks in anticipation o